Porous articles, and particularly porous metal articles such as castings and sintered metal parts, frequently must be sealed and impregnated (for simplicity, hereinafter generally referred to jointly as "sealed") before use. This is necessary to make the article capable of withstanding liquid or gas pressure during use, and also to increase its density, improve its strength, reduce corrosion, and frequently to prepare the surface of the article for a subsequent painting or plating operation. A wide variety of porous metal articles are used commercially today, and are manufactured from a wide variety of metals. Zinc, copper, brass, iron, aluminum, magnesium and various alloys are among the common metals needing to be sealed. Other important materials which frequently need to be sealed are wood and ceramics.
The prior art has recognized the need to seal these articles for many years. The earliest sealing process generally involved the use of either an inorganic sealant, such as sodium silicate, or a natural organic substance such as varnish. In more recent years, substances such as unsaturated alkyds, epoxides, and various other unsaturated monomers such as diallyl phthalate have been used. See, for example, U.S. Pat. No. 3,345,205 to Raech, issued Oct. 3, 1967, U.S. Pat. No. 2,932,583 to Grana, issued Apr. 12, 1960; and U.S. Pat. No. 2,554,254 to Kroft, issued May 22, 1951.
A substantially improved process for impregnating porous articles is taught by U.S. Pat. No. 3,672,942 to Neumann and Borowski, issued June 27, 1972, (the disclosure of which is incorporated herein by reference), which relates to impregnation with polymerizable anaerobic monomers, followed by surface treatment of the impregnated article with an organic solvent solution of an accelerator.
A major draw-back of the prior art systems is their need for organic solvent treatment to remove excess impregnant remaining on the surface of the article prior to cure, i.e., polymerization, of the impregnant. Use of solvents, of course, involves economic, toxicological and ecological disadvantages, for which reasons the search for aqueous-based substitutes has been vigorously pursued. Recent commercial systems have employed styrene-based polyester monomer impregnants which can be washed off the surface of articles by aqueous surfactant solutions; however, these monomers are not anaerobic and thus do not provide the substantial benefits associated with anaerobic impregnants, and the surfactant solutions must be used at elevated temperatures, e.g., about 150.degree. F. or higher, and for relatively long treatment times.
In copending application Ser. No. 467,989, filed May 8, 1974, now U.S. Pat. No. 3,969,552, patented July 13, 1976, to Frauenglass et al., there is disclosed an anaerobic impregnation process which advances the art by providing a surfactant-containing aqueous rinse which, for the first time, permitted use of an aqueous rinse with anaerobic monomers, which are quite water-insoluble. In practice, however, the Frauenglass et al. process is still not fully satisfactory for all uses. More specifically, that process does not remove well the excess anaerobic impregnant from the surface of very small areas which are not adequately reached by ordinary agitation. Typical of these difficult areas are small blind holes, e.g., about one millimeter or less in diameter and about 1 to 3 millimeters or more in depth, such as occur frequently in complex castings such as carburetors. An anaerobic impregnation composition which is inherently capable of being readily removed from such difficult areas by a simple aqueous rinse would be of great benefit to the impregnation industry.
It has now been found that anaerobic monomers suitable for impregnation may be rendered easily removable by incorporating in the monomer composition a surfactant of this invention. By so doing, the monomers are made self-emulsifiable upon contact with water, which greatly enhances the ability of plain water to rinse away surface deposits of anaerobic monomers from such troublesome areas as small blind holes.